Chickenpox is a highly contagious viral infection characterized by an itchy, blister-like rash. It is caused by the Varicella-Zoster Virus (VZV). Understanding this virus and its effects on human cells at a microscopic level provides insight into the disease.
The Varicella-Zoster Virus Up Close
The Varicella-Zoster Virus is too small to be seen with a conventional light microscope. Specialized tools, such as an electron microscope, are required to visualize it. When viewed this way, VZV appears as a roughly spherical particle.
At its core lies a double-stranded DNA genome, encased within an icosahedral capsid, a protein shell that gives the virus its geometric shape. This capsid is then surrounded by an outer lipid envelope derived from the host cell. Under the electron microscope, these layers appear as concentric circles.
How Chickenpox Affects Cells
While virus particles are invisible to a standard light microscope, the changes they induce in infected human cells are readily observable. Samples for microscopic examination are often obtained from the base of a skin lesion, such as a blister, through a Tzanck smear. This involves scraping cells from the lesion and placing them on a microscope slide for staining and analysis.
A hallmark finding under the light microscope is the presence of multinucleated giant cells, also called syncytia. These large, abnormal cells form when several infected cells fuse together due to the virus altering cell membranes. Their appearance indicates widespread viral activity within the tissue.
Another significant microscopic feature within infected cells are intranuclear inclusions, specifically Cowdry type A bodies. These are eosinophilic (pink-staining) structures found within the nucleus of infected cells, often surrounded by a clear halo. Their presence signifies sites of viral replication and assembly within the host cell’s nucleus.
The Role of Microscopy in Diagnosis
Microscopic examination plays a practical role in confirming a chickenpox diagnosis, especially when the clinical presentation is atypical. The Tzanck smear, by revealing characteristic cellular changes like multinucleated giant cells and intranuclear inclusions, can offer rapid confirmation of a herpesvirus infection, aiding clinicians in their assessment.
Other microscopic techniques can further refine the diagnosis. Direct fluorescent antibody (DFA) staining, for instance, involves using fluorescently tagged antibodies that bind specifically to viral antigens present in infected cells. When viewed under a fluorescent microscope, these cells glow, indicating the presence of viral proteins.
These microscopic methods are valuable for confirming the presence of a herpesvirus infection. However, while they confirm a virus from the herpes family, such as VZV, they may not definitively differentiate between VZV and other herpesviruses without additional, more specific laboratory tests.